Carl Pistorius is in intensive care after a head-on collision on a motorway in South Africa.

Oscar Pistorius’ brother Carl was critically injured in a car crash in South Africa.(Reuters)

Oscar Pistorius' brother has been critically injured in a head-on collision in South Africa.

Carl Pistorius, who has been a regular fixture in court during the brother's murder trial, is in a critical condition after a crash on the N1 motorway near Modimolle in Limpopo.

Carl is reported to have suffered multiple fractures after a car swerved out in front of him and collided with his vehicle.

He is believed to have been returning from a business trip from Polokwane and travelling in a convoy with a business partner on the N1 to Pretoria.

Family spokesperson Anneleise Burgess said Carl is "out of danger" but remains in intensive care after being transported to Pretoria hospital late last night, Sky News reported.

Burgess said traffic had backed up on the opposite side of the road when a car pulled out in front of Carl without warning.

The Pistorius family issued the following statement: "Carl was returning from a business trip to Polokwane. A colleague was following in a separate vehicle and witnessed the collision. He was able to tell us what happened."

In 2013, Carl was acquitted of culpable homicide and negligent driving after he was involved in a 2008 collision with motorcyclist Maria Barnard, who died six days after the incident.

The magistrate ruled that Barnard was driving her motorcycle excessively fast when she crashed into the back of Carl's vehicle.

Carl's case was brought to court shortly after his brother Oscar shot dead his model girlfriend Reeva Steenkamp on Valentine's Day. Oscar claims that she shot Steenkamp accidentally after mistaking her for a burglar.

The double amputee Olympian went on trial for murder in March and has pleaded not guilty to the charges, which could carry a life prison sentence.